This invention relates to the suppression of exhaust noise from internal combustion engines used to drive boats, particularly speed boats. Although adapted especially to jet-driven boats, this exhaust system is also effective with propeller-drive boats, it being a general objective of this invention to substantially suppress noise with a concealed system.
Heretofore, the standard exhaust systems for use with boats have used water-jacketed risers acting as traps to prevent backflow of water into the engine, combined with and/or followed by a muffler. These risers are characteristically U-shaped pipes extending well above the water line, and directed over or through the boat transom. And, there have been underwater exhausts used in outboard units and various inboard installations as well. However, it is an objective here to provide a noise suppression exhaust system for jet drives, and namely a "THROUGH JET EXHAUST" system that is highly effective, and a system that is concealed.
Replacing the usual water jacketed double-walled silencer chamber of the prior art, this invention provides a simplified expansion chamber with its internal surface cooled by means of water injection. In other words, the characteristic riser is replaced by a single noise suppressing expansion chamber, as distinguished from a water jacketed U-shaped exhaust pipe having no capability of noise suppression. With the present invention, an exhaust stack discharges upwardly into the expansion chamber for primary noise suppression, and a muffler element occupies the lower portion thereof for secondary noise suppression. An additional third stage of noise suppression is also gained by discharge of the exhaust through the jet mounting chest, which conceals it and puts it underwater at lower speeds. The water injection is from the engine coolant system, which is hot water that is sprayed onto the interior of the chamber where it is heated by the exhaust gases, the heat of exhaust converting a partial or substantial amount if not all of said water into steam vapor, or so that the water is discharged as a mist with the products of combustion.